asp.net qr code generator Part II The Core of ASP.NET MVC in VB.NET

Create QR Code in VB.NET Part II The Core of ASP.NET MVC

Part II The Core of ASP.NET MVC
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This code comes directly from the temporary files that ASP.NET creates on the Web server machine during execution. The root directory is located under Temporary ASP.NET Files, which in turn lives under the Windows Temp folder. The exact directory for your application is known only at run time and can be detected by watching the content of the System.Web .HttpRuntime.CodegenDir expression during a debug session. (See Figure 5-7.)
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FIGuRE 5-7 Detecting the run-time folder to snoop for details about the compilation of code blocks.
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Adding Logic to the View
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In ASP.NET Web Forms, the view (that is, the page) contains all the logic for both rendering and processing. In ASP.NET MVC, processing logic and rendering logic are distinct and belong to controllers and views. However, there s a gray area of logic that could belong to both processing and rendering. Sometimes it depends on the developer s vision of things; sometimes it s an architectural decision; sometimes it simply happens inadvertently. Let s recall a couple of guidelines that apply to the design of the view. The recommended approach when rendering views using ASP.NET MVC is to provide for all view data dependencies using only data that is explicitly provided through the view dictionary or, better yet from a design perspective, the view-model object. (You can provide data using both the dictionary and a strongly typed object.) In addition, the view should contain the least possible amount of logic that is not strictly related to rendering. For example, the following excerpt of markup is arguably the best option:
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< !-... <% int id = (int)ViewData[ ID ]; if (id == 0) { Html.RenderPartial( TOC , new TocViewModel(ViewData[ s ])); } else { Html.RenderPartial( Single , new ViewModel(ViewData[ ])); } %> Other markup here -->
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5 Inside Views
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The code first checks the value of an element in the view dictionary and then decides which partial view to render. This code, in particular, doesn t look bad and still relies only on provided data. However, it attributes some extra power to the view object. The view contains some logic deciding about the partial view to render that is not about the physical rendering of the view, such as a foreach statement. You should consider whether the decision about the partial view really belongs to the view. In general, it s preferable to move any logic up to the controller. The controller method that invokes the previous view, then, looks like this:
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public ActionResult s(int chapterID) { // Deal with input parameters int id = 0; if (chapterID.HasValue) id = chapterID.Value; // Perform any task, and acquire any data IContentServices service = ...; // Render the entire TOC if (id == 0) { IList<> chapters chapters = service.Loads(); return View("TOC", new TocViewModel(chapters)); } // Render details about a single chapter chapter = service.Load(id); return View("Single", new ViewModel(chapter)); }
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The net effect is that you now have two simpler views with a minimum amount of logic. If you have reasons to maintain partial views, you can use a view as simple as the one shown here:
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<!-... Html.RenderPartial("TOC"); Other markup here -->
The partial view automatically receives all the information you passed to the view, dictionary, and model. You can also restrict the information for the partial view if that best suits the needs of your application. A further optimization to the controller s method can be obtained using an internal method that encapsulates the logic to decide about which view to render:
public ActionResult Perform(object data) { // Deal with input parameters ...
Part II The Core of ASP.NET MVC
// Perform any task, and acquire any data ... // Render the entire TOC MyViewModel model = ...; return GetMethodView(model); } private ActionResult GetViewModel(MyViewModel model) { ... }
The View: Passive or Supervising
The MVC pattern that ASP.NET MVC is based on suggests the view be as thin and passive as possible. To reinforce the concept, the ASP.NET MVC tools in Visual Studio don t even add a code-behind file to each view you add. The message couldn t be clearer the thinner the better. This is the theory, however. In the real-world, a really passive view can be quite cumbersome to write and maintain and would add a lot of complexity to the controller. A thin view contains nearly no logic and inevitably takes you toward a multiplicity of smaller and extremely simple views. From here, the possible maintenance required could be a nightmare. If you opt for a passive view, you have an inherently more testable system because the logic in the view is reduced to an absolute minimum. Subsequently, you run no serious risk at all by not testing the view. Any piece of code can contain mistakes, but in the case of a passive view the extreme simplicity of the code allows only for gross and patent mistakes that can be easily caught without any automated procedure. In software, as well as in physics, a sort of conservation law applies. In physics, it s about the conservation of energy; in software it s about the conservation of complexity. So the complexity taken out of the view moves to another layer the controller and a passive view is inevitably coupled with a more complex controller. From here, you encounter the mantra these days as far as ASP.ENT MVC is concerned: thin view, fat model. In the end, opting for a passive view is a tradeoff between high testability and complexity of the controller classes. You can also opt for a more active view that contains some logic as far as data binding and data formatting is concerned. Developing a richer view might be easier, and it basically distributes the required complexity between the view and the controllers. The view needs to take care of some synchronization and adaptation work to make any input data usable by user interface elements. However, this code in an ASP.NET MVC scenario can only go into a server-side <script> tag. (In ASP.NET MVC , code-behind classes are still supported but kind of banned.)
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